The present invention concerns bicycles, and in particular concerns a bicycle frame having improved construction for better handling of shocks from rough terrain when using the bicycle and also improved construction to facilitate compact shipping and storing of the bicycle.
Conventional bicycles comprise a rigid frame including a center post in which a seat is mounted, a top cross bar rigidly connected to the center post near the top thereof and extending forwardly to a front journal tube in which the separate front wheel frame or fork is rotatably journaled, and a bottom cross bar which extends upwardly and forwardly from the bottom of the center post, usually from the crankshaft hub mounted at the bottom of the center post to the front journal hub at a point just below the top cross bar. The center post, top cross bar and bottom cross bar define the three legs of a rigid structural triangle.
In a revolutionary new bicycle disclosed in U.S. Pat. No. 4,669,747 and in improvement U.S. Pat. Nos. 4,792,150 and 5,080,384, the foregoing rigid triangularly-shaped frame member is eliminated. The bottom cross bar is eliminated all together and provisions for a flexible spring connection between the top cross bar and the center post are made. One or more tension cables extend from the front portion of the frame, near the front of the top cross bar, downwardly to a point at the rear portion of the frame near the bottom of the center post. This construction is especially well adapted to dirt bike racing and/or mountain bike racing in that the frame itself is designed to absorb the shocks of rough riding. Further, when pedaling torque spreads the frame, a second spring operably connected to the tension cable is compressed. At the end of the pedal stroke, the second spring relaxes and drives the crank upward for an extra kick when the pedals are on the upstroke part of their travel.
A problem has been that the tension cable, due to its non-rigid construction, can only control the flexural movement that results when the frame is spread. When the frame collapses (i.e. when the front and rear bicycle wheels move toward each other) the bending of the flexible spring connection is limited only by the strength of the flexible spring connection itself. Experience has shown that it is desirable to limit and/or control the flexural movement of the flexible spring connection in both directions. Further, testing has shown that it is desirable to transmit shocks from the front of the frame to the rear of the frame other than only through the flexible spring connection.
Aside from controlling the flexing movement of the frame during operation of the bicycle, there is a need to be able to easily reduce the bicycle frame to a compact arrangement for shipment and/or storage so that the bicycle can be more easily transported from place to place, such as in order to compete in races. Further, avid bikers are desirous of transporting the bike on vacations and other excursions. It is known to provide "quick release" wheels that can be quickly removed from a bicycle frame, however further reduction in the net size of the frame itself is desired so that freight/shipping costs are reduced.
Thus an improved bike frame solving the aforementioned problems is desired.